Puerto Penasco

I see a lot of folks are not current on the Mexican banking regulations.....There is a very STRICT control on the deposit of dollars by merchants and Mexican nationals, so MOST merchants will no longer take dollars, UNLESS they have easy access to an American bank.

Look at it this way. If this is a far south as you are going, dollars will be just fine.
The restaurants, fuel, vendors, etc will accept and/or make any conversion necessary.

Most stores and businesses, unless they are right on the border DO NOT accept U.S. dollars.. only Pesos.
Many of the Toll Booths have large signs "NO US Funds Accepted)
Another way to look at it is: "would you expect stores and businesses in the U.S. to accept Mexico Pesos?" of course not.
ATMs in Mexico only give Pesos.

Unless things have changed a whole lot, everyone prefers US dollars. Many if not most store owners are/where US retires.